Electron discharge device



y 1945- B. c. FLEMING-WILLIAMS 2,380,225

ELECTRON DISCHARGE DEVICE Filed Aug. 20, 1941 FIGO3 INVENTOR ATTORNEY Patented July 10, 1945 UNITED I STAT Es PATENT OFFICE This invention relates to electronbeamdeflection valves. -A valve of this kind usually com-.

prises anelectronbeam generating and focussing system, a pair of electrostatic deflector plates and a pairof target electrodes. Variation of the potential difference between the deflector plates produces variation of the proportion in which the beam current is divided between the target electrodes.

. In the arrangement according to .the invention, at least part of the focussing of the electron beam is effected by the deflector plates, while these simultaneously perform their normal function. a

If an electron beam is introduced between a pair of coaxial part-cylindrical electrodes, the inner one of which is maintained suflicientl'y positive with respect to the outer to cause the electron beam to follow the .curved path be-. tween them, then the field between the-electrodes will have a focussing effect upon the beam. If the beam is divergent from a point in the field between the electrodes, 'it will be brought substantially parallel after travelling between the electrodes through an' angle of. 63 degrees. Similarly,.if the beam is parallel at one position in the field between the electrodes, it will be brought approximately to a focus after. travelling through an angle of 63% degrees. Slight variations of the potential difference betweenthe electrodes will produce small changes in the positionsof the foci, but will not appreciably disturb the focussing effect. Q

An electron beam deflection valve according to the invention comprises apair of deflector plates in the form of co-axial part cylinders between which, superimposed on the varying deflection voltages, a steady potential diiference is maintained whereby the beam is made to pass along the arcuate path between the plates.

By this arrangement the electron beam generating and focussing system is made more simple and the total size of the. valve may be reduced. A high value of beam current can be employed for a given spacing of the deflector plates, and the degree of aberration 'which ocours in the focussing is remarkably low. It follows that a high value of mutual conductance is obtainable.

A beam of ribbon form is preferably employed, so arranged that its thickness liesin the radial direction of the deflector plates. By this means also a high mutual conductance is obtained.

In the accompanying-drawing Fig; is a diagrammatic longitudinal sectional view of an electron beam valve in which curved electrodes are used for focussing the beam, and Figs. 2 and 3 are similar views illustrating two: further embodiments of the invention.

A divergent ribbon electron beam is generated by the electrode system comprising cathode C, shield electrode G, and anode A. Anode A is a sheet electrode having a slot whose length lies perpendicular to the plane of the figure. Shield electrode G, and the active surface of cathode C, are each of part-cylindrical form and may. have their curvatures struck from the centre of the slot in anode A. Shield electrode G may, forexample, be maintained at the same .potential as cathode C (indicated in Fig. 1 as zero), and anode A may be maintained 400 volts positive to cathode C.

The ribbon beam diverges from a crossover which is of substantially line form, perpendicular tothe plane of the figure, and situated close to the slot of anode A. It then enters between deflector plates P1, P2. These plates are partcylindrical, and are co-axial about the axis 0, which is perpendicular to the plane of the figure. The angle XOY subtended by the plates at the axis 0 is somewhat less than 127, say 110. The bias potentials of plates P1 and P2 should be balanced about the potential of anode A, and must be such as to give the beam the necessary curvature to follow the arcuate path between plates P1 and P2. Potentials of about 480. and 320 volts positive to cathode may be found satisfactoryif the ratio of the radii of curvature of the plates is 4:5. I

The effective length of the plates, owing to fringing flux, is somewhat greater than the actual length. Also, in the valve illustrated, the beam diverges somewhat after leaving the crossover andbefore entering the field between plates P1 and P2. It will, therefore, become substantially parallel after following through an angle of rather less than 63 2 say about the curved path between the plates. It will then be caused to converge, but will not. yet have reached a focus when it leaves the field between the plates P1 and P2. It will, however, be convergent, and it will reach a focus at F1, not far from the emergent end of plates P1, P2. This will be. a line focus perpendicular to the, plane of the figure.

The precise values of the bias potentials are chosen to give. the beam the necessary curvature so that the focus F1 is formed on-the edge of the first target T1. Axial adiustmentof the position of this focus maybe effecteclby. adjust- .tween plates P1 and P2.

- bias voltage appropriate to its curvature.

ing the potential of a sheet electrode S having a slot sufficiently wide for the beam to be able to pass under all conditions of deflection. The primary purpose of electrode S is to serve as a suppressor to prevent secondary electrons generated at the targets T1, T2 from travelling towards the plates P1, P2, and for this purpose electrode S may have any potential somewhat below the lowest potential likely to be reached by either of the targets T1, T2 during operation If the potential of plate P1 is raised or lowered relatively to that of plate P2 by a few microvolts, the position of focus F1 is moved radially to a slight degree so that a greaterorless proportion of the beam current will impinge upon, and be collected by, the first target T1. The remainder of the beam current is collected by target T2 placed beyond T1. By way of example,-a push-pull input circuit is shown connected be- This is indicated as an alternating source B and a pair of impedances Z1 and Z2 connected in the leads from plates P1 and P2 respectively to their bias potential sources. Any suitable output circuit may be connected with the targets; for example, the impedances Z3 and Z4 in the leads to the targets provide a push-pull output between the terminals D.

By the placing of one target behind the other, provided the focus is fine on the edge of the first target, the deflection necessary to transfer the beam from one target to the other is reduced to a low value; in other words the mutual conductance is made high. The capacity between the targets is also reduced to a low value by this arrangement.

The targets are preferably of U-shape crossthe beam would diverge and again converge to a section, to discourage the emission of secondary I purposes hereinafter described. In Fig. 2, for

instance, an asymmetrical deflection voltage between plates P1 and P2 is indicated by the alternating source B1 in series with the lead of plate .P1 only. A second asymmetrical deflection voltage is applied to plates P3 and P4 by means of the alternating source B2 in series with plate P4 only. An asymmetrical output between the targets is indicated by impedance Z3 in the lead to the target T1 only.

If desired, one pair could be spaced considerably apart from the other, and the beam would then travel in a straight path between the pairs. If angle XOZ were about 60, the beam in passing between the pairs would be approximately parallel. If angle XOZ were smaller or larger, the beam would be divergent or convergent while passing between the pairs. The curvatures of the two pairs of plates need not be the same in degree or in sense provided that each pair has a Further subdivision of the plates could be effected if desired. Any tendency of the beam to diverge when travelling between one pair of plates and another could be overcome by the provision of a converging electron lens. i

If the plates were extended by another 127,

focus. This process may also be repeated more than once by still further extensions. The plates thus extended may be subdivided to any desired degree.

The beam need not necessarily enter between the plates as a divergent beam. It may, for example, be generated and focussed as a. parallel beam before entering between the plates. With plates of length subtending an angle of nearly 63%, say 55, the beam will then issue in form rapidly converging toward a focus. A similar result will be obtained if the plates are extended by another 127", so that they subtend an angle of about Also, the beam need not necessarily leave the plates in convergent form. Post-deflection focussing means may be provided to bring the beam to a fine focus on the edge of a target, if required.

If an electron beam deflection valve has more than one pair of plates arranged beside the beam like deflector plates for the same direction of the deflection, the output may be taken from one of these pairs of plates other than the first pair as shown in Fig. 3. The first pair of plates P1 and P2 are employed as deflector plates, the input deflection voltage being applied by source B as in Fig. 2. As the electron beam movesnearer to one plate and further from the other plateof a pair, a positive charge will appear on one of these plates and a negative charge on the other. 'A voltage therefore appears between the plates Pa and P4. The voltage is large when the deflection frequency is'high. The valve feeds energy to an output circuit connected between this pair of plates, here shown as an impedance Z5 connected to the plate P4, and the voltage is proportional to the velocity of the sideways movement of the beam. It follows that this method of obtaining the output from a beam deflection valve is particularly effective at the higher frequencies. A single target may be employed to collect the electron beam, which need not be brought to a focus. Alternatively, a pair of targets may be employed, the beam being focussed on the edge of one target in the ordinary manner, and between these targets there may be connected another output circuit, or a feedback or other desired circuit.

I claim:

1. In an electron beam deflection valve, an electron gun to generate a beam of electrons, said gun comprising a cathode and an electrode having only a single opening through which said beam passes, whereby said beam is focused to pass through a crossover and diverge therefrom, a focusing system including a pair of co-axial partcylindrical electrodes of different radii so arranged that they bound an arcuate space through which the beam passes and means to maintain a steady component of potential difference between said part-cylindrical electrodes to focus into a parallel beam the electrons issuing from said crossover, means to superimpose on said steady component a relatively small alternating component of potential difference to deflect said electrons, and means responsive to the deflection of said electrons to excite an output circuit in accordance therewith. 1

2. In an electron beam deflection valve, a plurality of electrodes including a final anode to generate a beam of electrons divergent from a concentrated source, at least one target electrode to collect said electrons, a pair of co-axial parton at least one of said steady components a rela-" tively small alternating component of potential difference to vary the position of the beam relative to said output electrodes toinduce an output voltage between them.-

3. In an electronbeam deflection. valve, means to generateand focus a beam of electrons to pass through a crossover and diverge therefrom, a focussing system including a pair of coaxial partcylindrical electrodes of different radii so arranged that they bound an arcuate spacethrough which the beam passes and means to maintain remainder of said electrons, a focussing system including a pairof co-axial part-cylindrical electrodes having radii in the approximate ratio of 4 :5 and so arranged that they bound an arcuate space through which the beam passes before reaching said first target electrode, means to maintain a steady component of potential difference between said electrodes to cause said electrons .to converge to a fine focus on the edge of said first target electrode, means to superimpose on said steady component a relatively small alternating component of potential difference to deflect said electrons, and an output circuit connected between said first and second target electrodes to respond to variations of the distribution of electrons between said target electrodes.

'7. In an electron beam deflection valve, means to generate a beam of electrons divergent from a concentrated source, a, focussing system including a plurality of co-axial part-cylindrical electrodes of different radii paired on opposite sides a steady component of potential difference between said electrodes to focus the electrons issuing from said crossover into a parallel beam, means for superimposing on said steady component an alternating component of potential difference to deflect said beam, a pair of output electrodes disposed on opposite sides of said beam beyond said first electrodes and an output circuit connected with said output electrodes and excited by the output voltage developed between them according to the position of said beam.

4. In an electron beam deflection valve, a plurality of electrodes including a final anode to generate and focus a beam of electrons to pass through a crossover and diverge therefrom, a first target electrode disposed in the path of said electrons to collect a part thereof, a second target electrode disposed in the path of said electrons beyond said first target to collect the remainder of said electrons, means comprising a pair of coaxial part-cylindrical deflector electrodes of different radii so arranged that they bound an arcuate space through which the beam passes,

. means to maintain substantially equal and opposite steady components of potential difference between each of said deflector electrodes and said final anode to cause said electrons to follow the arcuate path between them and to focus said electrons finely on the edge of said first target electrode, and means to superimpose on at least one of said steady components a relatively small alternating component of potential difference to vary the proportionate distribution of said electrons between said target electrodes.

5. In an electron beam deflection valve, means to generate a substantially parallel beam of electrons, a focussing system including a pair of coaxial part-cylindrical electrodes of difierent radii so arranged that they bound an arcuate space through which the beam passes, means to maintain a steady component of potential difference between said electrodes to cause said electrons to converge to a focus, means to deflect said beam of electrons, and an output circuit connected between said electrodes and excited by the output voltage induced between them by deflection of said beam.

6. In an electron beam deflection valve, means to generate a substantially parallel beam of electrons, a first target electrode disposed in the path of said electrons to collect a part thereof, a second target electrode disposed in the path of said electrons beyond said first target to collect the of said beam so that each pair of said electrodes bounds an arcuate space, means to maintain a steady component of potential difference between each pair of said electrodes to cause said beam to follow the curvature of each said space, means for superimposing a relatively small alternating component of potential difference between at least one pair of said electrodes to deflect said beam, and'means responsive to. the deflection of said beam for exciting an output circuit in ac-.

cor-dance therewith.

. 8. In an electron beam deflection valve, means to generate a beam of electrons divergent from a concentrated source, a focussing system including a plurality of coaxial part-cylindrical electrodes of different radii paired on opposite sides of said beam so that each pair of said electrodes bounds an arcuate space, means to maintain a steady component of potential difference between each pair of said electrodes to cause said beam to follow the curvature of each said space, means for superimposing one relatively small alternating component of potential difference between one pair of said electrodes, means for superimposing a diflerent relatively small alternating component of potential difference between another pair of said electrodes, and means responsive to the resultant deflection of said beam for exciting an output circuit in accordance therewith.

9. In an electron beam deflection valve, means to generate a beam of electrons divergent from a concentrated source, a focussing system including a plurality of co-axial part-cylindrical electrodes of different radii paired on opposite sides of said beain so that each pair of said electrodes bounds an arcuate space, means to maintain a steady component of potential difierence between each pair of said electrodes to cause said beam to follow the curvature of each said space, means to deflect said beam, and an output circuit connected between at least one pair of said electrodes and excited by the output voltage induced between them by deflection of said beam. 10. In an electron beam deflection valve, means for generating a beam of electrons divergent from a concentrated source, a focusing system including a pair of coaxial part-cylindrical electrodes of different radii so arranged that they bound an arcuate space through which the beam passes and means to maintain a steady component of potentialdifierence between said electrodes to focus the electrons from said source into a parallel beam, means for superimposing on said steady component'an alternating component of potential difference to deflect said beam, a pair of co-axial part-cylindrical output electrodes disposed on opposite sides of said beam beyond said focusing electrodes, and an output circuit connected with said output electrodes and excited by the output voltage developed between them according to the position of said .beam.

11. In an electron beam deflection valve, an electron gun to generate a beam of electrons, said gun comprising a cathode and an electrode having only a single opening through which said beampasses, whereby said beam is focused to pass through a crossover and diverge therefrom, a focusing system including a pair of co-axial part-cylindrical electrodes of different radii so arranged that they bound an arcuate space through which the beam passes'and means to maintain a steady component of potential difference between said part-cylindrical electrodes to focus the electrons from said source into a parallel beam, means for superimposing on said steady component an alternating component of potential difierence to deflect said beam, a pair of output electrodes comprising targets disposed one beyond the other in the path of said beam beyond said part-cylindrical electrodes, and an output circuit connected with said output electrodes and excited by the output voltage developed between them according to the position of said beam.

'12. In an electron beam deflection valve; a plurality of electrodes including a final anode to generate and focus a beam of electrons to pass through acrossover situated close to said final anode, a focusing system comprising a pair of co-axial part-cylindrical electrodes of different radii so arranged that they bound an arcuate space through which said beam passes after passing through said crossover, a first target electrode disposed in the path of said beam to collect part of the electrons thereof and so situated that the edge of said target and said final anode subtend an angle of approximately 127 at the common axis of said part-cylindrical electrodes, a second target electrode disposed in the path of said beam beyond said first target to collect the remainder of the electrons thereof, means to maintain a steady component of potential difference between said part-cylindrical electrodes to focus said beam finely on said edge of said first target electrode, means to 'superimpose on said steady component a relatively small alternating component of potential difference to deflect said beam and to vary the proportionate distribution of the electrons of said beam between said target electrodes, and an output circuit connected between said target electrode.

BRIAN CLIFFORD FLEMING-WILLIAMS. 

